Concrete blocks, such as used to construct retaining walls, can either be “pre-cast,” also known as “wet-cast,” or “dry-cast” blocks. Wet-cast blocks are blocks that are formed from concrete having a water-cement ratio of about 0.4 or higher. In the wet-casting process, the concrete must cure in the mold before it is removed, usually by disassembling the mold. In contrast, dry-cast blocks are formed from “zero-slump” concrete, typically using a high speed block-forming machine.
The main advantage of dry casting is that concrete components can be mass produced at a high rate using a block-forming machine. Since the blocks can be stripped from the mold immediately (without curing), a single mold can be used to mass produce a specific component at a much greater rate than is possible with wet casting. The size, shape and texture of dry-cast blocks however are limited by the block-forming machine and the equipment used to convey and store the blocks during the curing process, such as the pallets that support the blocks after they are removed from the mold. For example, most block-forming machines are not compatible with a mold greater than 12 inches in height. In addition, blocks greater than 24 inches in width or depth tend to cause the pallets supporting the uncured blocks (after being removed from the mold) to deflect under the weight of the blocks, allowing the blocks to deform. Thus, concrete blocks having greater dimensions typically must be manufactured using a wet-casting process.
The main advantage of wet-cast blocks is that the concrete has a higher density, lower porosity, and higher cement to aggregate ratio, resulting in higher freeze-thaw resistance than dry-cast blocks. As such, wet-cast blocks are preferred or required in geographic areas where the blocks frequently are exposed to freeze-thaw conditions. Another advantage of wet casting is that the blocks can be molded to have virtually any size, shape and/or texture.
There are several known wet-cast retaining wall systems that are used to construct structural retaining walls. These systems tend to include massive, wet-cast concrete blocks that weigh several thousands of pounds. As can be appreciated, such blocks are expensive to produce and are much more difficult to transport to a jobsite and install compared to relatively smaller dry-cast retaining wall blocks.
What is needed is a wet-cast retaining wall system having blocks that are easier to produce, transport and install and provide greater flexibility in the types of construction techniques that can be used to construct walls.